In the past, silicon crystals have been grown from the melt using both the well-known Czochralski crystal growth process and, more recently, the Heat Exchanger Method of crystal growth described in U.S. Pat. Nos. 3,653,432 and 3,898,051 (both of which patents are hereby incorporated by reference). In such processes, serious problems of silicon carbide impurity have been encountered when attempting to grow crystals at pressures below about 30 torr.